Component for preventing arc-erosion in the terminal structure of a fused cutout



June 1965 R. J. BRONIKOWSKI 3,188,432

COMPONENT FOR PREVENTING ARC-EROSION IN THE TERMINAL STRUCTURE OF A FUSED CUTOUT Flled May 31. 1960 [iii IN V EN TOR. Ray/770774! Jfiramfioa/skd BY 3 3 E Z fitz'orng in 2a ,3 f0

United States Patent 3,188,432 COMPONENT FOR PREVENTING ARC-ERGSIGN IN THE TERMINAL TRUCTURE OF A. FUSED CUTOUT Raymond J. Bronikowski, South Milwaukee, Wis,

- assignor to McGraw-Edison Company, Milwaukee,

Wis., a corporation of Delaware Filed May 31, 19%, Ser. No. 32,977 7 Claims. (Cl. 290-127) This invention relates to electric circuit interrupters in general, and more particularly to a fuse construction which will interrupt high magnitude fault currents an increased number of times before requiring replacement of the fuse cartridge and terminal member.

Although the invention is hereinafter disclosed as embodied in an open fuse cutout having an expulsion type fuse, it will be apparent to persons skilled in the art that the invention may also .be used with other types of fuse cutouts.

The purpose of a fuse cutout is to interrupt fault current through the rupture of a fusible element and subsequently to extinguish the electrical are drawn as a result of the rupture. Once the arc has been extinguished the fuse has performed it primary function and is relatively useless until it has been refused, and in the case of dropout fuse cutout constructions, replaced in circuit bridging position.

Extinction of the electrical arc is generally accomplished by widening the gap between the ends of the ruptured link and by quenching the arc with gases evolved from the fuse tube as a result of the temperature increase within the tube due to the electrical arcing. Since considerable pressure build up takes place in the fuse tube as result of the evolved gases, recent developments in the art have concentrated on improved techniques of venting the fuse tube to avoid rupture of the tube and to remove ionized gases from the vicinity of the arc.

One generally accepted method of accomplishing this is an expendable cap disclosed by Jepsen et al., Patent No. 2,702,842, issued February 22, 1955 and assigned to the assignee of the instant invention, which serves to normally close one end of the fuse tube. During low amperage fault current operation the cap serves to maintain one end of the fuse tube closed while the gases are vented from the other end of the tube to clear the arc. However, the cap is so constructed that during high current fault conditions the cap respond to the increased gas pressure within the tube by rupturing and thereby providing additional venting at that end of the tube.

While this construction necessitates replacing the expendable cap as well as the fuse link the cost of this is compensated for by the selectivity and increased protective capabilities of the lepsen device, as witnessed by its general acceptability by the electrical industry;

Prior art devices which incorporate the above construction, in general, utilize a contact terminal which sun rounds one end of the fuse cartridge and which contains an integral metal portion extending from the end of the cartridge. The bore of said portion communicates With the bore of the fuse tube and serves as an extension of the fuse tube bore. The expendable cap is then generally positioned atop the integral metal portion of the contact to close one end of the fuse tube.

This construction has proven adequate for most previous electrical installations, however, with the advent of increasing capacities of power distribution systems, present type fuse constructions are becoming inadequate. I have found that prior art fuse constructions when utilized in the'area of 15 kv. and 16,000 amps, or higher do not perform adequately. When these constructions are subject to electrical conditions in this area the bore of the upper metallic terminal member suffers considerable erosion due to the destructive effects of arcing and due to the flow of high speed, hot gas therethru, after rupture of the fusible element. If the fault conditions are high in value the upper end of the terminal member may erode entirely thru, thusly destroying the terminal member and perhaps the fuse cartridge. Even if the erosion is not suflicient, under a given electrical condition, to destroy the upper terminal member, repeated electrical conditions of this magnitude will result in destruction of this member. Erosion of the terminal member, in the vicinity of the area where the expendable cap is afilxed thereto, may so weaken this area that the cap and a portion of the terminal member may be blown outwardly under the impetus of gas pressure within the fuse cartridge, at current values that would not normally require expulsion of the cap. At higher currents in prior art devices where the cap would normally be expended the erosion of the terminal member may lead to an irregular gas flow pattern which causes flashover. This erosion of component parts of the cutout in addition to involving costly replacement and installation expenditures can also interfere with the proper operation of the cutout.

Another disadvantage of prior art devices is that an arc established in the tube frequently vaporized the metal on the inner bore of the upper terminal member thereby leaving the bore of the metal terminal member in a rough irregular condition causing turbulence in the gases passing outwardly of the cartridge adjacent the terminal. This turbulence causes a non-smooth irregular flow of ionized gases from the terminal portion and in many cases this ionized gas, as it passes outwardly in the venting of the upper terminal, drifts down toward the lower terminal and permits external flashover between the upper and lower terminal members exteriorly of the tube.

It is therefore, an object of the present invention to provide a fuse construction that will substantially eliminate the erosive effects of high tempcraturehigh velocity gas flow occurring during interruption of extremely high fault current,

Another object of the present invention is to provide a fuse construction that will require a minimal amount of replacement parts after a number of high current interruption-s.

Another object of the present invention is to provide a fuse construction that will vent gases at at least one end of the fuse tube with a minimum of turbulence thereby substantially eliminating fiashover between terminals externally of the fuse tube.

These and other objects of the invention will become more apparent upon consideration of the following description of the preferred embodiments of the invention taken in connection with the accompanying drawings in which:

FIG. 1 is a vertical elevation of a portion of a fuse cutout of one type which may contain an embodiment of the invention.

FIG. 2 is a partial side elevation of a fuse cartridge assembly with a portion cut away illustrating the invention.

FIG. 3 is a partial side elevation of a fuse cartridge assembly with a portion cut away illustrating a slightly modified form of the invention.

Referring now to FIG. 1 of the drawings, a fuse cutout 8 is shown having a fuse cartridge 10 mounted thereon and a lower terminal member 11 which is adapted to be pivotally supported on a fuse support 9. The lower terminal 11 is shown embracing the fuse cartridge but the particular mechanical relationship of terminal .1 1 to fuse cartridge do is not to be considered a limitation on the invention disclosed herein.

tube 12 may be a sleeve insert or may be molded to the interior of the fuse cartridge and may be of organic fiber, or any other material that will evolve a substantial volume of deionizing gases at a given temperature. It is also conceivable and within the scope of this invention to pro- 1 vide a single fuse tube that will resist bursting and evolve gases at a predetermined temperature. Screw threads 13 or similar means may be provided around the upper extremity of the fuse cartridge 16 for reasons which will be subsequently explained.

A circular metal electrode member 14 having an aperture 15 therein is positioned atop the fuse cartridge and gas evolving fuse tube 12 so that aperture communicates with the bore 12a of .the gas evolving fuse tube 12.

The electrode member 114 may be of any electrically conductive material that has substantial resistance to are erosion and is preferably in the form of a stainless steel washer.

An upper terminal contact member 1-6 having a longitudinal bore .17 therein is affixed to and surrounds the upper portion of fuse cartridge 10. Inner screw threads 18 in the bore 17 of contact member 16 engage with external screw threads 13 on the fuse cartridge to firmly attach con tact member 16 and fuse cartridge 10. While a threaded engagement is described as aflixing the terminal member 16 to the cartridge 10 other fastening means such as cement or a set screw (not shown) or any combination thereof may be utilized. The upper portion of contact member 216 terminates in a cylindrical portion 19 having a longitudinal bore 241 therethrough which is of a somewhat lesser diameter than the bore 17 and in concentric relationship thereto. At the upper end of the threaded bore 17 of terminal member 16 is an inwardly projecting annular shoulder portion 21 which bears upon the upper face of the electrode member 14. It can thusly be seen that when the terminal member 16 is firmly attached to the fuse cartridge .10 by means of screw threads 13 and 13 or other means that shoulder 21 serves to bias electrode member 14 tightly against the end of the fuse cartridge assembly. In this respect it should be noted that by properly machining shoulder 21 of contact '16, a washer-like seat could be provided which could serve as an electrode and thereby replace electrode 14 :but this is not shown.

An insulating sleeve member 23 is positioned within the bore 20 of the portion 19 on the contact member 16 and extends forsubstantially the full length of the bore 20. The sleeve 23 may be cemented to the interior of cylindrical portion 19 as by an epoxy resin or the like but this is not shown; One end of the insulating sleeve member 23 terminates at the shoulder portion 21 of the terminal member 16 so that when the terminal member is firmly affixed to thefuse cartridge 10 the sleeve '23 bears tightly against a portion of the upper surface of the electrode 14. The

other end of the sleeve 23 terminates at and is tightly in contact with an inwardly projecting annular shoulder 24 on the upper end of the portion 19. The upper side of annular shoulder 24'; also serves as a seat for the button head 25 of a fuse link 26. The fuse link 26 extends from the button head 25 through the bore 20, aperture 15 and through the bore 12a and outwardly of fuse cartridge 10 at the lower end thereof to the lower terminal 11 and is affixed thereto as by means 22.

The outer surface of the portion 19 on the upper contact 16 is threaded at 27 near the upper extremity thereof. A cap 28 having a frangible portion 28 and having internal screw threads 29 for engagement with the threads 27 is affixed to the upper end of the portion 19.

While a frangible expendable cap is described as enclosing one end of the fuse tube a multiple piece cap (not shown) or other pressure responsive means may be utilized as long as venting is accomplished during high current fault conditions. Other means than a screw connection between the portion 19 and cap 28 may be utilized although the disclosed construction is much preferred.

The terminal member 16 may also have a contact surface 7 30 and hook stick engaging means 31 associated therewith, on opposite sides of the fuse cartridge.

Materials that may be utilized in fabricating the insulating sleeve member 23 must have a high resistance to the erosion effects caused by high current fault interruption and must also be able to resist cumulative erosion caused by repeated interruption of fault currents of this nature. Materials that will meet both of these requirements include asbestos phenolic, glass phenolic, boron nitride and Supramica 500. (A trademark of the Mycalex Company for a compression molded, machinable,

ceramopla-stic made with synthetic mica.)

The member 23 may be a sleeve insert or may comprise an insulating coating or molding applied to the bore 2d of the ferrule 19 without deviating from the perview of the invention. Additionally while the bore of the insulating sleeve is shown as being substantially straight it may also be diverging or converging-diverging or any combination thereof without deviating from the objects and general spirit of the invention but this is not shown in order to shorten the disclosure and to facilitate the understanding thereof.

In FIG. 3 a slight modification of the invention is described. This modification involves the use of a plurality of sealing rings 32 between the peripheral end portions of insulating sleeve 23 and the bore 20 of the portion 1) of the terminal contact 16. These rings 32 are described as being separate insulating members, but may be raised portions of the insulating sleeve 23, the purpose of which is to prevent gas flow behind the sleeve member, i.e., between sleeve 23 and ferrule 19 during fault current interruption.

In FIG. 3 a link protector tube 33 surrounds the upper extremity of the fuse link 26 and serves to con-fine low current arcing to the confines thereof and which burst-s on high over currents. A tube such as tube 33 is well known in the art and may be utilized with both embodiments of this invention though it does not of itself form any part of this invention. a

In practice in both embodiments when a high fault current is initiated the temperature of the fusible portion 26 of the fuse link is increased to the melting temperature and the link ruptures and arcing begins between the ruptured ends of the fuse link.

As arcing continues the heat generated by the arc causes decomposition of the inner surface of the gas evolving fuse tube 12 and the turbulent high pressure gas so developed effects an expulsive force which attempts to break up the arc. As the arc and gas resist each other, an equillbrium arc position is established. Pressure in the tube builds up rapidly and the gas begins to vent from the bottom of the tube. If the pressure in the tube continues to build up as a result of temperature rise and gas evolution caused by the electrical arcing, the frangible portion 28' of expendable cap 28 will blow off and venting from the top of the tube takes place. As arcing continues the arc is transferred from the upper portion of the ruptured fuse link to electrode 14 and arcing then takes, place between the electrode and lower portion of the ruptured fuse link.

Since very little arcing has taken place in the interior of the ferruleportion 1Q protected by the sleeve member 23 the surface of sleeve 23 will remain smooth and free of defects and thusly will provide an uninterrupted surface over which the escaping gases may pass. I have found that gases flowing over this surface will not assume a turbulent state as would be the case if the sleeve were eliminated and that these non-turbulent gases do not have the tendency to drift downwardly to the lower terminal 11, thereby mitigating external tube flashover which heretofore has been a problem in the case of unlined members.

The hot gases passing through sleeve 23 also will not cause insulating material to be torn from the sleeve as would be the case with no sleeve member present where a large amount of conducting material would be torn away from the terminal member due to the action of the hot gases.

The inwardly extending shoulder 24 of portion 19 is provided to serve as a seat for the button head end of the fuse link 26 and to promote heat dissipation and cooling during normal continuous load currents. In interrupting high current fault conditions the arc will be drawn, as explained, between the electrode 14 and the lower end of the ruptured fuse link. Ininterupting exceptionally high, and not often encountered fault currents, some erosion of the shoulder 24 may take place over a period of time. However this will not occur to such an extent that a new terminal member will be required before other portions of the fuse cutout wear out.

Very few fuse cutouts will ever be called upon to interrupt maximum rated fault conditions five or more times during their lifetime and hence any slight erosion that may take place in shoulder 24 is more than compensated for by the heat dissipation and cooling advantages of the shoulder.

The arcing electrode 14 serves to confine an electrical arc within the fuse tube 12 as well as preventing burning of the portion 19 from occurring at the junction of fuse cartridge and insulating sleeve 23.

In this connection the insulating sealing rings 32 (FIG. 3) between the sleeve and inner bore of portion 19 serve the purpose of providing sealing strength in addition to that provided by the electrode 14.

The invention herein contained has been found to materially reduce metal erosion of the upper terminal member under single and repeated current interruptions. In this manner the interrupting rating of a given cutout may be increased considerably since this is based on successful interruption of at least five maximum over current conditions. Thusly the fuse construction described herein is capable of longer life than present constructions and capable of interrupting higher fault currents a greater number of times than present devices.

The nozzle effect (permitting smooth gas flow) of the sleeve member 23, due to its resistance to erosion as compared to ferrules without insulating liners, aids the evolved gases to escape once the expendable cap has blown. Another important aspects of the insulating sleeve as compared to unlined ferrules, is that no metal is vaporized therefrom during and immediately after arcing and therefore the flow of gases from the end of the ferrule will be less turbulent in nature. Further since metal vapor is generally more highly ionized than the other gases present, the absence of such, occasioned thru the use of the insulating liner, will decrease the tendency of arc maintenance and will also substantially eliminate the tendency of the expelled gases to drift or blow toward external conducting members thereby causing external tube fiashover. The latter advantage is due to both the lower degree of ionization present in the gases as well as to the smooth substantially uneroded liner surface which imparts little turbulence to the escaping gases. In this manner the electrical device to be protected is further safeguarded.

Another advantage that has accrued from my invention is that the functioning of the expendable closure means will be unaffected over a period of time as the portion 19 of the contact terminal 16, will never, in ordinary usage, become weaker than the frangible section of the cap or other expulsion means thereby avoiding premature expulsion.

Although the invention has been described in considerable detail it is to be understood that such description is intended as illustrative rather than limiting as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

1. A fuse cutout device comprising, in combination, an elongated generally hollow fuse tube, rupturable fuse link means, electrically conductive terminal means supported at one end of said fuse tube, said fuse link means connected to said terminal means and extending into said fuse tube and said fuse tube being subject to a build-up of a gaseous media therein as a result of rupture of said fuse link means, said electrically conductive terminal means including a bore communicating with said one end of said fuse tube to provide a passage for discharge of said gaseous media, pressure sensitive means normally closing said one end of said fuse tube and operative, in response to a build-up of gaseous media in said fuse tube, to open said fuse tube end for discharge of said gaseous media, and means disposed in said bore beyond said fuse tube end and characterized by being resistant to the are drawn when said fuse link means ruptures and to said gaseous media, said means in said bore extending around the inner bore surface to protect said terminal means from said are and gaseous media.

2. The combination of claim 1 including an arcing elec trode electrically connected to said terminal means and exposed to the interior of said fuse tube, said arcing electrode positioned intermediate said one fuse tube end and said means in said bore to remove said are to said arcing electrode and from the vicinity of said means in said bore during current interruption.

3. A fuse cutout device comprising, in combination, a generally elongated fuse tube, rupturable fuse link means, electrically conductive means on one end of said fuse tube defining a terminal for connection with said fuse link means, said rupturable fuse link means connected to said terminal and extending into said fuse tube and said fuse tube being subject to a build-up of a gaseous media therein as a result of rupture of said fuse link means, said electrically conductive means also defining a passage communicating with the interior of said fuse tube for discharging said gaseous media therethrough, pressure sensitive means normally closing said passage and operative in response to build-up of said gaseous media in said fuse tube to open said passage for discharge of said gaseous media, and means arranged in said passage intermediate the end of said fuse tube and said pressure sensitive means and characterized by being resistant to both the flow of said gaseous media and said are so that said means in said passage protects said electrically conductive means from said gaseous media and are.

4. The combination of claim 3 wherein said means in said passage extends over and covers the entire portion of said passage between said terminal and fuse tube.

5. The combination of claim 4 including an arcing electrode connected to said electrically conductive means and arranged inter-mediate said means in said passage and fuse tube and exposed to the interior of said passage and fuse tube so that the are drawn upon rupture of said fuse link means is removed from said terminal to said arcing electrode and from the vicinity of said insulating means.

6. In a fuse cutout device, the combination with a generally hollow gas evolving fuse tube having a rupturable fuse link therein and subject to a build-up of a gaseous media therein as a result of rupture of said fuse link of, terminal means supported at one end of said fuse tube and including an elongated bore having one end communicating with the interior of said fuse tube and extending axially therefrom, said terminal means including a radially inwardly projecting flange positioned at the opposite end of said bore to provide a point of electrical connection for one end of said fuse link, pressure sensitive means positioned at and normally closing said opposite end of said bore and operative, in response to said build-up of gaseous media in said fuse tube, to open said fuse tube end for discharge of said gaseous media, and a tubular member characterized by being resistant to the are drawn upon rupture of said fuse link and the fiow of said gaseous media and positioned within said bore between said radial flange and said one end of said here so that substantially the entire inner surface of said bore is protected from said are and the discharge of said gaseous media, and an arcing electrode electrically connected to said terminal means and positioned at saidfone end of said bore, said arcing electrode being exposed to the interior of said fuse tube to remove said arc to said arcing electrode and from the Vicinity of said insulating means during current interruptionf 7. The combination of claim 6 including sealing means positioned intermediate said tubular member and said hore'to prevent leakage of said gaseous media behind said tubular member.

References Cited by the Examiner UNITED STATES PATENTS 1,687,232 10/28 Steinmayer 200 127 15 1,955,138 4/34 Managan 200-127 2,013,427 9/35 Starr 200-127 8 2,094,013 9/37 Hill 200-127 2,135,787 11/38 Birkenmaier 200-127 2,137,270 11/33 Crump 200 127 2,278,058 3/42 Bowie 200 127 2,328,825 9/43 McMahon 200-149 2,329,642 95/43 Mosley 200-121 2,351,969 6/44 Hurst zoo-113 2,460,967 2/49 Amundsen 200-114 2,702,842 2/55 Jepsen et al. 200-127 2,798,133 7/57 Curtis 200-127 2,878,341 3/59 Lange 200-120 FOREIGN PATENTS 5,171 3/06 Great Britain.

BERNARD A. GILHEANY, Primary Examiner. RICHARD WOOD, Examiner. 

1. A FUSE CUTOUT DEVICE COMPRISING, IN COMBINATION, AN ELONGATED GENERALLY HOLLOW FUSE TUBE, RUPTURABLE FUSE LINK MEANS, ELECTRICALLY CONDUCTIVE TERMINAL MEANS SUPPORTED AT ONE END OF SAID FUSE TUBE, SAID FUSE LINK MEANS CONNECTED TO SAID TERMINAL MEANS AND EXTENDING INTO SAID FUSE TUBE AND SAID FUSE TUBE BEING SUBJECT TO A BUILD-UP OF A GASEOUS MEDIA THEREIN AS A RESULT OF RUPTURE OF SAID FUSE LINK MEANS, SAID ELECTRICALLY CONDUCTIVE TERMINAL MEANS INCLUDING A BORE COMMUNICATING WITH SAID ONE END OF SAID FUSE TUBE TO PROVIDE A PASSAGE FOR DISCHARGE OF SAID GASEOUS MEDIA, PRESSURE SENSITIVE MEANS NORMALLY 